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    <H1 CLASS="title">File Descriptors</H1>
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<DL class="page-index">
  <DT><A href="#overview">Overview</A></DT>
  <DT><A href="#acknowledgments">Acknowledments</A></DT>
  <DT><A href="#installation">Installation</A></DT>
  <DT><A href="#headers">Headers</A></DT>
  <DT><A href="#reference">Reference</A>
    <UL>
      <LI CLASS="square"><A href="#file_descriptor_source">Class <CODE>file_descriptor_source</CODE></A></LI>
      <LI CLASS="square"><A href="#file_descriptor_sink">Class <CODE>file_descriptor_sink</CODE></A></LI>
      <LI CLASS="square"><A href="#file_descriptor">Class <CODE>file_descriptor</CODE></A></LI>
    </UL>
  </DT>
</DL>

<HR>

<A NAME="overview"></A>
<H2>Overview</H2>

<P>
    The classes <CODE>file_descriptor_source</CODE>, <CODE>file_descriptor_sink</CODE> and <CODE>file_descriptor</CODE> provide file access via operating system file handles or file descriptors. These <A HREF="../guide/concepts.html#device_concepts">Devices</A> behave much like the <A HREF="file.html">File Wrappers</A> <CODE>basic_file_source</CODE>, <CODE>basic_file_sink</CODE> and <CODE>basic_file</CODE>, with the following important differences:
</P>
<UL>
    <LI CLASS="square">A file descriptor Device may be constructed from a file descriptor which is already open.
    <LI CLASS="square">The only <A HREF="../guide/buffering.html">buffering</A> is provded by the Boost Iostreams library.
    <LI CLASS="square">There is no automatic line-ending conversion.
    <LI CLASS="square">Wide-character streams are not supported. 
</UL>

<P>
    When a file descriptor Device is copied, the result represents the same underlying file descriptor. The underlying file descriptor is <I>not</I> duplicated. 
</P>

<P>
    The classes <CODE>file_descriptor</CODE> supports 64-bit seek offsets whenever they are supported by the underlying operating system or runtime library. Currently, file descriptor Devices may not work corectly with file descriptors opened in non-blocking mode.
</P>

<P>
    Line-ending conversion can be provided, if desired, using the class <A HREF="newline_filter.html"><CODE>newline_filter</CODE></A>. Wide-character versions of the file descriptor Devices may be defined as follows, using the template <A HREF="code_converter.html"><CODE>code_converter</CODE></A>:
    <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/code_converter.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/code_converter.hpp&gt;</SPAN></A>
    <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/device/file_descriptor.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/maped_file.hpp&gt;</SPAN></A>

    <SPAN CLASS='keyword'>typedef</SPAN> code_converter&lt;file_descriptor_source&gt;  wfile_descriptor_source;
    <SPAN CLASS='keyword'>typedef</SPAN> code_converter&lt;file_descriptor_sink&gt;    wfile_descriptor_sink;</PRE>
</P>

<A NAME="acknowledgments"></A>
<H2>Acknowledgments</H2>

<P>
    The file descriptor Devices are based on work of Nicolai Josuttis  (<A CLASS="bib_ref" HREF="../bibliography.html#josuttis1">[Josuttis1]</A> <I>pp.</I> 672-3 and <A CLASS="bib_ref" HREF="../bibliography.html#josuttis2">[Josuttis2]</A>).
</P>

<A NAME="installation"></A>
<H2>Installation</H2>

<P>
    The file descriptor Devices depends on the source file <A CLASS="header" HREF="../../src/file_descriptor.cpp"><CODE>&lt;libs/iostreams/src/file_descriptor.cpp&gt;</CODE></A>, which makes use of Windows or POSIX headers depending on the user's operating system. For installation instructions see <A HREF="../installation.html">Installation</A>.
</P>

<A NAME="headers"></A>
<H2>Headers</H2>

<DL class="page-index">
  <DT><A CLASS="header" HREF="../../../../boost/iostreams/device/file_descriptor.hpp"><CODE>&lt;boost/iostreams/device/file_descriptor.hpp&gt;</CODE></A></DT>
</DL>


<A NAME="reference"></A>
<H2>Reference</H2>

<A NAME="file_descriptor_source"></A>
<H3>Class <CODE>file_descriptor_source</CODE></H3>

<H4>Description</H4>

<P>Model of <A HREF="../concepts/device.html">SeekableSource</A> and <A HREF="../concepts/closable.html">Closable</A> providing read-only access to a file through an operating system file descriptor.</P>

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">enum</SPAN> file_descriptor_flags {
    never_close_handle,
    close_handle
};

<SPAN CLASS="keyword">class</SPAN> file_descriptor_source {
<SPAN CLASS="keyword">public</SPAN>:
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN>                      char_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  handle_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  category;
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                            std::ios_base::open_mode mode = 
                                std::ios_base::in );
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_source_ctor">file_descriptor_source</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_open">open</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in );
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );   

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );   

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">bool</SPAN> <A CLASS="documented" HREF="#file_descriptor_source_is_open">is_open</A>() <SPAN CLASS="keyword">const</SPAN>;

    handle_type <A CLASS="documented" HREF="#file_descriptor_source_handle">handle</A>() <SPAN CLASS="keyword">const</SPAN>;
};

} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>

<A NAME="file_descriptor_source_ctor"></A>
<H4><CODE>file_descriptor_source::file_descriptor_source</CODE></H4>

<PRE CLASS="broken_ie">    file_descriptor_source();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    file_descriptor_source( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                            std::ios_base::open_mode mode = 
                                std::ios_base::in );
    file_descriptor_source( <SPAN CLASS="keyword">int </SPAN>fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    file_descriptor_source( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    file_descriptor_source( <SPAN CLASS="keyword">int </SPAN>fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    file_descriptor_source( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>
<P>
    The first member constructs an empty <CODE>file_descriptor_source</CODE>.
</P>

<P>
    The second member constructs a <CODE>file_descriptor_source</CODE> to access the file with the given pathname. <CODE>Path</CODE> should be either a string or a Boost.Filesystem path. The parameter <CODE>mode</CODE> has the same interpretation as <CODE>(mode | std::ios_base::in)</CODE> in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A>
</P>

<P>
    The third member constructs a <CODE>file_descriptor_source</CODE> to access the file with the given operating system or runtime-library file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the <CODE>file_descriptor_source</CODE> being constructed &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The fourth member is the same as the third, except that it accepts a Windows file handle instead of a file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the <CODE>file_descriptor_source</CODE> being constructed &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The deprecated members are there to provide backwards compatability with old versions.
    To use them you need to define <CODE>BOOST_IOSTREAMS_USE_DEPRECATED</CODE>.
    The descriptor is always closed by <CODE>close</CODE> but only closed in destructors if <CODE>close_on_exit</CODE> is <CODE>true</CODE>.
</P>

<A NAME="file_descriptor_source_open"></A>
<H4><CODE>file_descriptor_source::open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in );
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>

<P>
    The parameters of <CODE>open</CODE> the same as those of the corresponding constructors.
    If the file descriptor already holds a file, it'll be closed
    (unless opened or constructed with <CODE>never_close_handle</CODE>).
</P>

<A NAME="file_descriptor_source_is_open"></A>
<H4><CODE>file_descriptor_source::is_open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">bool</SPAN> is_open() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns <CODE>true</CODE> if the underlying file was opened successfully.</P>

<A NAME="file_descriptor_source_handle"></A>
<H4><CODE>file_descriptor_source::handle</CODE></H4>

<PRE CLASS="broken_ie">    handle_type handle() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns the underlying OS file descriptor.  On Windows, this is a <CODE>HANDLE</CODE>.  On other systems, it is an <CODE><SPAN CLASS="keyword">int</SPAN></CODE>.</P>

<A NAME="file_descriptor_sink"></A>
<H3>Class <CODE>file_descriptor_sink</CODE></H3>

<H4>Description</H4>

<P>Model of <A HREF="../concepts/device.html">SeekableSink</A> and <A HREF="../concepts/closable.html">Closable</A> providing write-only access to a file through an operating system file descriptor.

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">enum</SPAN> file_descriptor_flags {
    never_close_handle,
    close_handle
};

<SPAN CLASS="keyword">class</SPAN> file_descriptor_sink {
<SPAN CLASS="keyword">public</SPAN>:
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN>                      char_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  handle_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  category;
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                          std::ios_base::open_mode mode = 
                              std::ios_base::out );
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_sink_ctor">file_descriptor_sink</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_open">open</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::out );
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );   

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );   

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">bool</SPAN> <A CLASS="documented" HREF="#file_descriptor_sink_is_open">is_open</A>() <SPAN CLASS="keyword">const</SPAN>;

    handle_type <A CLASS="documented" HREF="#file_descriptor_sink_handle">handle</A>() <SPAN CLASS="keyword">const</SPAN>;
};

} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>

<A NAME="file_descriptor_sink_ctor"></A>
<H4><CODE>file_descriptor_sink::file_descriptor_sink</CODE></H4>

<PRE CLASS="broken_ie">    file_descriptor_sink();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    file_descriptor_sink( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                          std::ios_base::open_mode mode = 
                              std::ios_base::out );
    file_descriptor_sink( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    file_descriptor_sink( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    file_descriptor_sink( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    file_descriptor_sink( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>

<P>
    The first member constructs an empty <CODE>file_descriptor_sink</CODE>.
</P>

<P>
    The second member constructs a <CODE>file_descriptor_sink</CODE> to access the file with the given pathname. <CODE>Path</CODE> should be either a string or a Boost.Filesystem path. The parameter <CODE>mode</CODE> has the same interpretation as <CODE>(mode | std::ios_base::out)</CODE> in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref2" HREF="#note_1"><SUP>[1]</SUP></A>
</P>

<P>
    The third member constructs a <CODE>file_descriptor_sink</CODE> to access the file with the given operating system or runtime-library file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the <CODE>file_descriptor_sink</CODE> being constructed &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The fourth member is the same as the third, except that it accepts a Windows file handle instead of a file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the <CODE>file_descriptor_sink</CODE> being constructed &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The deprecated members are there to provide backwards compatability with old versions.
    To use them you need to define <CODE>BOOST_IOSTREAMS_USE_DEPRECATED</CODE>.
    The descriptor is always closed by <CODE>close</CODE> but only closed in destructors if <CODE>close_on_exit</CODE> is <CODE>true</CODE>.
</P>

<A NAME="file_descriptor_sink_open"></A>
<H4><CODE>file_descriptor_sink::open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::out );
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>

<P>
    The parameters of <CODE>open</CODE> the same as those of the corresponding constructors.
    If the file descriptor already holds a file, it'll be closed
    (unless opened or constructed with <CODE>never_close_handle</CODE>).
</P>

<A NAME="file_descriptor_sink_is_open"></A>
<H4><CODE>file_descriptor_sink::is_open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">bool</SPAN> is_open() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns <CODE>true</CODE> if the underlying file was opened successfully.</P>

<A NAME="file_descriptor_sink_handle"></A>
<H4><CODE>file_descriptor_sink::handle</CODE></H4>

<PRE CLASS="broken_ie">    handle_type handle() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns the underlying OS file descriptor.  On Windows, this is a <CODE>HANDLE</CODE>.  On other systems, it is an <CODE><SPAN CLASS="keyword">int</SPAN></CODE>.</P>

<A NAME="file_descriptor"></A>
<H3>Class <CODE>file_descriptor</CODE></H3>

<H4>Description</H4>

<P>Model of <A HREF="../concepts/seekable_device.html">SeekableDevice</A> and <A HREF="../concepts/closable.html">Closable</A> providing read-write access to a file through an operating system file descriptor.

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">enum</SPAN> file_descriptor_flags {
    never_close_handle,
    close_handle
};

<SPAN CLASS="keyword">class</SPAN> file_descriptor {
<SPAN CLASS="keyword">public</SPAN>:
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN>                      char_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  handle_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>  category;
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in | std::ios_base::out );
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );   

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <A CLASS="documented" HREF="#file_descriptor_constructor">file_descriptor</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_open">open</A>( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in | std::ios_base::out );
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );   

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_open">open</A>( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );   

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#file_descriptor_open">open</A>( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS="keyword">bool</SPAN> <A CLASS="documented" HREF="#file_descriptor_is_open">is_open</A>() <SPAN CLASS="keyword">const</SPAN>;

    handle_type <A CLASS="documented" HREF="#file_descriptor_handle">handle</A>() <SPAN CLASS="keyword">const</SPAN>;
};

} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>

<A NAME="file_descriptor_constructor"></A>
<H4><CODE>file_descriptor::file_descriptor</CODE></H4>

<PRE CLASS="broken_ie">    file_descriptor();
    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    file_descriptor( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in | std::ios_base::out );
    file_descriptor( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    file_descriptor( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    file_descriptor( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    file_descriptor( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>

<P>
    The first member constructs an empty <CODE>file_descriptor</CODE>.
</P>

<P>
    The second member constructs a <CODE>file_descriptor</CODE> to access the file with the given pathname. <CODE>Path</CODE> should be either a string or a Boost.Filesystem path. The parameter <CODE>mode</CODE> has the same interpretation as in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref3" HREF="#note_1"><SUP>[1]</SUP></A>
</P>

<P>
    The third member constructs a <CODE>file_descriptor</CODE> to access the file with the given operating system or runtime-library file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the <CODE>file_descriptor</CODE> being constructed &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The fourth member is the same as the third, except that it accepts a Windows file handle instead of a file descriptor.
    If the second argument is <CODE>close_handle</CODE>, the file descriptor is closed when the new <CODE>file_descriptor</CODE> &#8212; or one of its copies &#8212; is closed or destructed.
</P>

<P>
    The deprecated members are there to provide backwards compatability with old versions.
    To use them you need to define <CODE>BOOST_IOSTREAMS_USE_DEPRECATED</CODE>.
    The descriptor is always closed by <CODE>close</CODE> but only closed in destructors if <CODE>close_on_exit</CODE> is <CODE>true</CODE>.
</P>

<A NAME="file_descriptor_open"></A>
<H4><CODE>file_descriptor::open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Path&gt;
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">const</SPAN> Path&amp; pathname,
                     std::ios_base::open_mode mode = 
                         std::ios_base::in | std::ios_base::out );
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">file_descriptor_flags</SPAN> );

    <SPAN CLASS='comment'>// Deprecated</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );

    <SPAN CLASS='comment'>// Deprecated, Windows-only</SPAN>
    <SPAN CLASS="keyword">void</SPAN> open( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>

<P>
    The parameters of <CODE>open</CODE> the same as those of the corresponding constructors.
    If the file descriptor already holds a file, it'll be closed
    (unless opened or constructed with <CODE>never_close_handle</CODE>).
</P>

<A NAME="file_descriptor_is_open"></A>
<H4><CODE>file_descriptor::is_open</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">bool</SPAN> is_open() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns <CODE><SPAN CLASS="keyword">true</SPAN></CODE> if the underlying file was opened successfully.</P>

<A NAME="file_descriptor_handle"></A>
<H4><CODE>file_descriptor::handle</CODE></H4>

<PRE CLASS="broken_ie">    handle_type handle() <SPAN CLASS="keyword">const</SPAN>;</PRE>
    
<P>Returns the underlying OS file descriptor.  On Windows, this is a <CODE>HANDLE</CODE>.  On other systems, it is an <CODE><SPAN CLASS="keyword">int</SPAN></CODE>.</P>

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<P>
    <A CLASS="footnote_ref" NAME="note_1" HREF="#note_1_ref"><SUP>[1]</SUP></A><A CLASS="bib_ref" HREF="../bibliography.html#iso">[I<SPAN STYLE="font-size:80%">SO</SPAN>]</A>, Table 92. 
</P>

<!-- End Footnotes -->

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<P CLASS="copyright"> 
    Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
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